Mixers are provided with a variety of configurations. Some mixers, for example, have stirrers which adversely affect the microstructure of the medium to be agitated, especially by a shear action and have been found not be useful for some kinds of biological system where cell disruption is a drawback. For mixing in systems in which tissue or cell damage may occur or mixing blades may disrupt biological materials or have an adverse effect on the mixture, it is known to provide an oscillating drive for the vessel which may be a shaker vessel or the like and which can impart an oscillatory movement to the object carrier or vessel. The oscillatory movement can be a linear movement or a rotary movement. These mixers generally operate with frequencies up to 20 Hz. Ultrasonic mixers have been provided heretofore as well and these generally operate at frequencies of 20 kHz or higher.